Method of forming laminated pressure vessels



Sept. 9, 1952 D. B. ROSSHEIM 2,609,595

METHOD OF FORMING LAMINATED PRESSURE vEssELs Filed May 18, 1948 3 Sheets-Sheet 1 INVENTOR.

DAVID B. ROSSHEIM ATTORNEYS Sept. 9, 1952 0. B. ROSSHEIM 2,609,595

METHOD OF FORMING LAMINATED PRESSURE VESSELS Filed May 18, 1948 3 Sheets-Sheet 2 INVENTOR. DAVID B. ROSSHEIM F's. 7 /i wf A 7' TORNEVS Sept. 9, 1952 D. B. ROSSHEIM METHOD 6F FORMING LAMINATED PRESSURE VESSELS 3 Sheets-Sheet 3 Filed May 18, 1948 INVENTOR. DAVID B.ROSSHEIM Evy, f 1

ATTORNEYS disadvantages.

Patented Sept. 9, 195 2 STATES PATENT orrics 7 METHOD or FORMING LAMINATED i PRESSURE VESSELS David 'B. Rossheim, Teaneck, N. J., assignor, to .The M. W. Kellogg Company, Jersey City, N; J

a corporation of New Jersey Application May 18, 1948, Serial No. 27,805

, 1' This invention relates to the manufacture of pressure vessels, and more particularly relates to methods of'manu'facturing multi-layer pressure vessels adapted for industrial *use and capable of withstanding high pressures.

Claims. (Cl. 29-4482) Prior to the present invention, several different methods have been employed to fabricate high pressure vessels. These methods included forging the vessel from a single ingot; laminating. a plurality of concentric layers for forming one layer upon another; spirally winding a lon sheet of metal to build up a plurality of layers; reinforcing an inner shell by means of windings of wire, cable, or strapping; making up a plurality of shells, the shells being separately formed and after formation being assembled to form the vessel.

All of these prior methods presented certain For example, forging is extremely expensive and time consuming, requires heavy and expensive equipment and highly skilled labor. When the pressure vessels are fabricated by forming concentric layerone upon another and by spirally winding a sheet of metal, only relatively short lengths can be made; also it is extremely difficult, if not impossible, to inspect the welds by X-ray, and furthermore it is very difficult to accurately pre-stress the various layers. Windings of wire, cable, or strapping normally impart no longitudinalstreng-th to the vessel, and if they are formed to interlock so that they will add longitudinal strength their formation and application becomes an expensive and highly-skilled operation. In the past when pressure vessels were assembled from separately formed shells it was extremely diificult, if not impossible, to vpre-stress the various layers witjh'any degree "of accuracy and furthermore it was often necessary to machine the inner and outer surfaces of each shell to close tolerances to insurefliassembly and support of the inner shells by the outer shells.

The present invention is an improvement of the method wherein a lurality of shells are separately formedand then assembled 'to form a multi-layer vessel. In practicing the present invention any degree of pre-stress is easily and accurately-obtained in any'of the layers;'it is not necessary to machine any of the surfaces of any of the shells; the vessels can be fabricated in. relatively long lengths thus eliminating the need, in most applications, to welda plurality of fabricated lengths together; the welds, if any, in each shell can be accurately and completely inspected before assembly, and eaeh layer of the assembly adds to the longitudinal strength of the vessel.

relatively fast and economical. Y

One object of the present invention is to provide a method for the manufacture of multilayer pressure vessels whereby predetermined stresses can be accurately established in predetermined layers. Another object of the present invention is to provide a method for the manufacture of multilayer pressure vessels wherein a plurality of shells are fabricated separately and assembled one over the other and whereby any predetermined degree of stress can be accurately established in any layer.

Another object of the present invention is to provide a method for the manufacture of multilayer pressure vessels by fabricating a plurality of shells separately and assembling said shell one over the other wherein it is not necessary to machine said shell-s before assembly and whereby any predetermined degree of stress can be accurately established in any layer.

Another object of the present invention is to provide a method for the manufacture of multilayer pressure vessel-s by providing a plurality of shells and assembling said shells successively one over the other wherein it is' not necessary to machine said shells before assembly and whereby the interface surfaces of said shells are brought into face-to-face contact by successively drawing predetermined areas of one or more of said shells.

Another object of the present invention is to provide a method for the manufacture of multilayer pressure vessels by providing a plurality of shells and assembling said shells successively one over the other wherein it is not necessary to andorder of one orm o'reof such stepswith respect to each of the others which are exemplified in the following detailed disclosure and the ,cated in theclaims.

scope of the application of'whichfwill be indi- For a fuller understanding of the nature and Fig. 3 is a diagrammatic longitudinal sectional makes possible the prevention of undesired dis tortion such as localized thinning out of the shell, buckling, or uneven upsetting, and also makes it possible to heat said areas evenly and accurately. The individual shells can be fabricated in any desired manner, as for example,by forging, or by bending fiat plates into cylindrical form and welding their abutting edges together, or if desired prefabricated pipe or tubing can be used. It

view showing a layer in the process of being assembled on a partly fabricated pressure vessel by a being drawn to reduce its diameter;

Fig. 4 is a diagrammatic longitudinal sectional view showing a layer in the process of being assembled on a partly fabricated pressure vessel by being drawn in a different manner toreduce its diameter;

Fig. 5 is a diagrammatic longitudinal sectional view showing a layer being assembled on a partly fabricated pressure vessel by upsetting circumferential increments of said layer;

Fig. 6 is a diagrammatic longitudinal sectional view showing a layer being assembled on a partly fabricated pressure vessel by upsetting circumferential increments of said layer in a different manner;

Fig. 7 is a diagrammatic end view showing a layer being assembled on a partly fabricated pressure vessel byupsetting longitudinal increments of said layer; and,

Figs. 8 and 9 are diagrammatic perspective views showing a layer being assembled on a partly fabricated pressure vessel by upsetting longitudinal increments of said layer in a, different manner.

The process of the present invention comprises the steps of providing two or more shells capable of being concentrically assembled one within the other, assembling two of the shells one Within the other, and causing their interface surfaces to be progressively brought into face-to-face contact with each other. The shells can be progressively brought into face-to-face contact by successively heating relatively narrow circumferential bands on the outside shell and successively subjecting the areas thus heated to an axial tension to draw said heated portions and thus progressively cause the diameter of the shell to be reduced. The shells can also be progressively brought into face-to-face contact by successively heating relatively narrow areas of either the outer shell or the inner shell and successively subjecting the areas thus heated to a compressive force to cause said areas to be upset a predetermined amount to progressively reduce the internal diameter and increase the outside diameter of the shell being upset.

The above mentioned areas, whether circumferential bands or longitudinal areas, are heated to a temperature at which the material from which the shell is formed is relatively plastic and is capable of a uniform plastic flow when subjected to a predetermined tensile or compressive loading. The areas are so heated that they are substantially the same temperatur throughout their width, and the. temperature is so controlled that there is an abrupt temperature drop in the material adjacent thereto, so that said adjacent material has Sufiicient'rlgidity to withstand the stress to which the shells are subjected without permanent deformation.

The areas heated are narrow so that a hi-h degree of control over the plastic flow of the heated material is possible at all times. This welds, if any, be dressed smooth.

is not necessary that the various shells be machined; it is only necessary that they be fabricated to reasonable close tolerances and that the Inasmuch as each shell is fabricated before it is assembled in the pressure vessel, it is possible to inspect all welds and other portions of each shell thoroughly to insure maximum strengths in each shell. All of the shells can be stress relieved and/or heat treated before being assembled on th pressure vessel.

Fig. 1 is a longitudinal sectional view of a multilayer pressure vessel fabricated by the process of the instant invention. The pressure vessel comprises an inner shell 18 having a pair of hemispherical ends or head's l2 attached thereto by circumferential welds i l. Either one of the heads 12, or both of them, can be provided with a connector l3. Inner shell I0 and a portion of each of the heads [2 are encompassed by tightly'fitting outer layers l6, l8 and 29. Each of the layers l2, l 6, l8 and 2B in the completed vessel are preferably pie-stressed so that they are under a predetermined condition of circumferential compression or tension. For example, the pressure vessel of Fig. 1, preferably has layers 10 and 15 under circumferential compression and layers 18 and 20 under circumferential tension so that each layer, when the vessel is subjected to its working pressure, will withstand its proportional share of said pressure. Inner shell I 0 and heads 12 can be formed from any material having the desired properties for the service for which the vessel is intended as, for example, stainless steel. The outer layers l6, l8 and 2|), which are not in contact with the contents of the vessel, can be formed of less expensive material having the necessary strength.

When a hemispherical head is employed it is preferably designed and constructed to have a thickness sufiicient to withstand the total stress to which it will be subjected, with its outside diameter substantially equal to the outside diameter of inner shell 18. If the-thickness of such a head is rea'ter than the thickness of the inner shell 10, its inner surface can be faired off so that its ed es are substantially the same thickness as the thickness of the inner shell l0. Outer shells and are weldedthereto by welds l9 and 2!. The

ends of the shells l6. l8 and 29 can be made to extend over any desired length of the heads 12.

If material has been removed from the heads 2 to fair them oif, the ends will extend over said heads 12 a sufficient distance to reinforce them in those areas where material has been removed.

The ends of shells IE1, l8 and 29 also assist the welds it to withstand the axial load to which they plurality of reinforcing shells 26, 28

are subjected by reason of pressure exerted on said heads l2 by the contents of the vessel.

Fig. 2 is afragmentary sectional view of a different type of multi-layer pressure vessel fabricated by the process of the instant invention. The pressure vessel of Fig. 2 comprises an outer 'shell'lz'having heads 24 welded thereto, anda and 30 lo- .catedinside of shell 22'.

It will be understood, however, that the present invention is not limited to themanufacture of multi-layer'vessels comprising four layers, but that it may be employed to manufacture vessels having any desired number of layers. It will also be'understood that any desired type of head can be incorporated in the multi-layer pressure vessels, and that the heads can be welded or otherwise attached to the cylindrical body of the vessel after it has been fabricated. i

Fig. 3vdiscloses the 'multi -layer pressure vessel of Fig. 1- in the processiof being manufactured by one modification of the present invention. In the modification disclosed the outer shell 16 is being brought into face-to-face contact with the inner shell ill by being drawn to reduce its diameter. r d.

After the inner shell lll'i'has been fabricated, heads l2 are welded to its ends, the welded joints therein are ground smooth, all desired inspections are performed and'the entire unit may be stress relieved and/or heat treated in any desired manner. Outer shell I6 is next fabricated, its welded joints are ground smooth and the entire shell is inspected and, if desired, stress relieved, and/or heat treated'in any desired man:

ner.: Shell 16 is fabricated to have an inner diameter .as nearly the same as the external diameter of the inner shell l0 as possible and still beable to slip over shell I0.

Ifv it is desired to fabricate a pressure vessel of greater length than the length of plate material available for forming the various shells thereof, or longer than .available lengths of ,pipe, a plurality of short shells can be welded together, end to end, before the different layers are assembled together, to obtain shells of the desired length. 'If this is done each weld will preferably be ground smooth, inspected, and repaired if necessary, before the layers are assembledone over the other.

7 Shell I6 is slipped over inner shell 10 and positioned with respect to shell I!) so that the end 32 extends beyond one end of shell ID the distance it is desired to have said shell [6 overlie ing load. The other end 38 of shell 16 is similarly attached by means of lugs 36 to a jig or'fixture 40 which is connected by means of shaft 42 to a hydraulic cylinder (not shown) or any other mechanism for subjecting the shell l6 to a high degreeof tension.

A ring burner 44 having, orforming, a plurality of oxyacetylene orifices or nozzles 46, extends around the shell and is capable of being moved longitudinally along said shell -l6. The

"nozzles 46 carried, or formed,-by ring 44 are evenly and closely spaced around said ring 44, and can be spaced thereon in a plurahty of rows sq that the burner will heat a band of the desired width while remaining stationary, or the ring can be oscillated back and forth along shell Hi to heat the desired width of-band. The burner 44 is of such a diameter that nozzles 46 are adjacent to but spaced'from the outer surface of shell I6 so that they can efficiently and evenly heat throughout its width a predetermined circumferential narrow band of shell l6. Cooling rings 48 are located oneach side of ring 44 and function to keep the shell [6, on each side of the circumferential area heated by ring 44, cool enough to resist permanent deformation by the above mentioned tension. It is preferred that the ring burner 44 comprise a heating means similar to the oxyacetylene heating means disclosed in the copending application Serial Number 679,900 of David B. Rossheim et al., filed June 28, 1946, for Method of Shaping Thermoplastic Bodies, now issued as Patent Number'2,480,774. However, any means, as for example, high frequency induction heaters or' resistance heaters, capable of evenly and rapidly applying a large amount of heat to a predetermined narrowarea may be employed. It is also preferred that'cooling rings-48 be similar to the cooling means disclosed in the above mentioned copending application Serial Number 679,900, now Patent No. 2,480,774, butany other suitable cooling means, as, for example, solid metal rings or waterfspray, may be used.

Aftershell I6 is attached to fixtures 34 and 40, ring burner 44 is moved adjacent to fixture 34 or to a point opposite weld l4 and the oxyacetylene nozzles 46 are ignited to heat a narrow circumferential band of predetermined width-on shell l6 to a predetermined temperature at'which the desired degree of plasticity is attained. When shell I6 is formed of low carbon steel, it has been found that heating the "circumferential bands to approximately 1400 F'. results in said bands attaining the desired. degree of plasticity.

When the'desired temperature is attained, ring burner 44 and cooling means 48are slowly moved cation, Serial Number 679,900, now Patent No.

2,480,774 before the burner 44 is moved. Thismay be necessary, or desirabla as explained in copending application, Serial Number 679,900, now Patent No. 2,480,774, to raise the temperature of the material on each side of the circumferential band to the temperature that it will be at after the process has been in operation a period of time and has reached equilibrium. As soon as the desired temperature is attained, a predetermined tensile load is applied to the shell l6 through the fixture 40 by means of the above mentioned hydraulic cylinder, or other means, to cause a uniform plastic fiow to take place in the material comprising the heated area of shell 16 whereby said area is elongated and at'the same time reduced in diameter. The elongation andireduction in diameter causes the inner surface of shell l6 to be brought into contactwith the outer surface of shell Ill. The predetermined tensile load is maintained on shell I6 as ring burner 44 advances from end 32 to end 38 sothat the elongationand reduction in diameter or shell It takes place continuously.

I Fig. 4 illustrates another manner in which the outer layers can be applied to the inner shell by rawin a u er sh l o re u e i ame e Heads 12a, similar to heads 12 of Fig. 3 are welded to inner shell. We and outer shell 16a is fitted over shell Illa, and heads. 12a. One end of shell Ito is constricted so that its inner surface conforms to the outer surface of one of the heads 12a, and tha a d is welded by weld Ila to its adjacent head {2a. The end of shell lGa can be constricted to conform to head i211. either before or after shell 15a is placed over shell Illa. il oollar 50 is placed against the other head I211 and a flange 52 is welded to the other end of shell [6a. Flange 52 is threaded to carry a plurality of jacking screws 54 which engage the ollar 50- A u ner, an cooling rings similar to those disclosed in Figs. 3, are provided. ,Whenthe circumferential band on shell l6a has been heated tothe desired temperature, in the manner disclosed in connection with Fig, 3, a longitudinal tensile load is applied to shell Him by screwing the jacking screws 54 inwardly against collar 50 to cause the heated band to be drawn and reduced in diameter. The tensile load can be maintainedsubstantially constant on length of shell [a so that the two shells are in intimate face-to-faee contact, flange 52 is cut from shell [Ba and that end-of the shell is constricted to engage the outer surface of its adjacent head 12a and is welded thereto.

7. The predetermined tensile load which is ap- I. plied to shell 16 or |6a will vary wit the Wall thicknessand diameter of said shell,,the reduction in diameter that is-desired and the pressure that shell or [Go is to apply to shell or Illa.

It will be apparent that'the circumferential band can be heated to a temperature higher or lower than 1400 F. if it is so desired. If a higher temperature is employed, a smaller tensile load will be applied to the shell. If a lower temperature is employed, a greater tensile load will be applied to the shell. However, the temperature cannot be lowered to a point where the necessary tensile load will cause a permanent deformation in thematerial adjacent to the heated band.

= The width of the circumferential band which is heated is as narrow as possible consistent with obtaining the desired reduction in diameter thereof and the desired pressure on shell Hl or 18a. By so doing, the plastic flow of the material comprising the heated circumferential band is 1 under substantially complete control at alltimes, thus permitting shell 16 or I60: to-be progressively brought into contact with shell I I) or Na in small increments, thus insuring complete contact of all interface areas on the two shells, and making possible the avoidance of localized thinning out and undesireddistortion. It has been found that best-results are obtained when the width of the heated band is equalto or slightly greater than the thickness of the shell. However, in cases when shells l6 or;l6c are formed of thin material, this .condition'ca-nnot be obtained due to mechanical limitationsof the heating means and satisfactory results can be obtained with a heated bandof greater relative width. v

Whereas, it is preferred to continuously ad- Vance ring burner 44 while at the same time continuously applying a tensile load to shells L6 or lSa, it will be understood that theproce is can he carried out by intermittently heatin a circumferential area of said shells followed by the application of a tensile load t the shell to elonate and reduce the diameter thereof in the heated area, followedhy heating a succeeding, or slightly overlapping, 'areaand'reducing said succeeding area. It will also be understood that the tensile load can be applied to shell IE or 16c before the circumferential area thereon ll'ia'sattained the desired temperature and maintained until said temperature is reached and the desired elongation and reduction in diameter obtained. Also, the heating can be startedfatany' point on shell 16 that is between theen'ds of shell" llland continued first in one direction and then the other to bring theinterface surfaces into contact'with each other. I

It will also be appreciated that any desired predetermined circumferential tension can be established in shell 16 or 16a by controlling the tension to which saigl'shell is subjected and thus controlling the pressureexerted thereby on shell in or Illa clue to the reduction in diameter of shell leer Isa- Shells la and 20 can be applied o'ver shells 1B or {6a and i8 respectively in the same manner that shell H5 or "5a is applied to shell I ll. Any desired number of shells can be built up in this manner, and the stress that each succeeding shell exerts on the inners'hells can be accurately predetermined, as above described, by varying the tensile load employed to reduce their diameter. Preferably, eachsucceedi igshell is applied'so that it exerts a greater circumferential pressure on the preceding shell than said preceding shell exerted on its ownpre ceding shell. Thus, it is possibleto fabricate a'multi-ljayer pressure vessel wherein ,a predetermined number of the inner layers are under circumferential tension, said tension and compressions beingofjsuch magnitudes that the maximum strength of each layer of the vessel is fully utilized to withstand the pressure contained by the vessel.

'Fig. 5 illustrates anotherv embodiment of the present invention wherein each succeeding outer shell of a multi-layer pressure vessel is applied thereto by successively upsetting predetermined circumferential areas of each shell. I After inner shell JDb has been fabricated and inspected it 15 placed in a vertical position 'upon an anvil or rigid base 56, and shell l6b is placed around shell lilb and als rested on anvil 56. 3 Shell l6b s of greater length than inner shell I 8b, and therefore its upper end extends beyond the end 0f shell lllb, and is engaged by piston 58 which is attached to a hydraulic press (not shown) or other means for applying alongitudinal compressive load to shell- 15b. Ring burner 44 carrying orifices or nozzles llfi, and cooling rings 4 8, surround shell lfib. W

Rin burner .44 is placed adjacent the lower end of shell 16b, the nozzles are ignited and per mitted to heat a narrowcircumferential bandfof predetermined width on 16b. This vbandislicated, for similar materials, to .thesame temperatrue as the modification of Fig.3, i. afloatproximately 14-00" F. It maybe necessary; or desirable, to heat and cool the first circumferential band several times, in the manner set forth above connection with Fig. 3, to raise the temperature of the material adjacent the heated band to the temperature that it willbe at after the process has been in operation a period of tune and has reached equilibrium. When the desired temperature has been attained. ring burner 44 and cooling means 48 are moved slowly upward towards piston .58 at such a rate that said burner-will'constantly have under its flame a circumferential band of the predetermined Width which is at substantially the predetermined desired temperature throughout its width. As soon as the circumferential band reaches the desired temperature and at the same time that ring burner 44 is started moving, a predetermined longitudinal compressive load is applied to shell I6b through piston 58. by means of the above mentioned hydraulic press, or other means, to cause a uniform plastic flow to take place in the material comprising the heated'band whereby saidband is upset. The predetermined compressive load is maintained onshell IBb as ring burner 44 advances along shell I61), and the pressure thus applied causes the upsetting of said shell I6 b,-to takeplace continuously, thus successively thickening predetermined areas of the walls of shell I6b and decreasing the inside diameter thereof and causing the inner surface thereofpto press against the outer surface of shell IIlb. .It is-preferred to continuously-advance ring burner 44 while at the same timecontinuously applying a compressive force to shell I6b thus making the upsetting a continuous operation. However, it will be understood thatthe upsetting can be carried out intermittently by heating a circumferential area of shell I6b followed by the application of the compressive force to upset the heated portion, followed by heating'and upsetting an adjacent, or slightly over-lapping area, and so on until the full length of shell IBb has beenupset. Also the heating can be started at any point on shell I6b that is between the ends of shell Illb and continued first in one direction and then the other to bring the interface surfaces into contact with each other. v

It is important in practicing this modification of the invention thatthe only substantial permanent deformation of shell I6b be upsetting which is the result of plastic flow. Due to practical considerations it is almost impossible to upset relatively long lengths of shell I622, or' any subsequent shell in one step, without buckling occurring; It was disclosed in the above mentioned copending application Serial Number 679,900, that thermoplastic materials may be deformed under compression as a result of plastic flow of the material, and substantially complete control maintained over said plastic flow so that substantially no deformation from buckling results, if the width of the area heated is from one-half toone-quarter, and less, the natural buckling wave length of the material being deformed at the temperature to which the area is heated. This principle is employed in the present invention to give substantially complete control of the plastic flow of the material comprising the shell being upset. Therefore, the circumferential band that is heated on shell l6b is preferably from one-half to one-quarter, and less, the natural bucklingwave length of the material of said shell I6b at the temperature to which the band is heated. It is preferred to keep the width of the heated band less than one-half the buckling wave length whenever possible inasmuch as heated bands Wider than this permit a slight amount of buckling. The amount of buckling, however, does not become objectionable until the width of the heated band exceeds three-quarters of the natural buckling wave length. It is therefore possible, in cases where it is impracticable or undesirable to keep. the width of the heated circumferential band less than half the buckling wave length, to heat a circumferential band having a width that does not exceed three-quarters of said buckling wave length. Y

The cooling rings 48 function in the same manner in this modification as they doin the modification of Fig. 3, i. e., they maintain a sharpv drop in temperature between the edges of the heated band and the rest of shell I6b to keep the shell on each side of the heated area cool enough to resist permanent deformation by the above mentioned compression. The predetermined compressive force which is applied-to shell I6b will vary with the wall thickness and diameter of said shell, the amount of upsetting that is desired, and the pressure that shell I6b is to apply to shell IUb. Any predetermined desired circumferential compression can be established in shell I6b by applying the proper compressive force to said shell I 6b to bring about the above described upsetting. The amount of upsetting that takes place in the heated circumferential band varies with the compressive force which causes the upsetting. Therefore, the higher thecompressive force which isapplied longitudinally to shell Hill the greater will be the amount of upsetting, and the more shell I to is upset the greater is the circumferential compressive force which it exerts on shell IIlb. It will be'apparent that the circumferential band can be heated to a temperature higher or lower than 1400 F. if it is so desired. If a high temperature is employed, a smaller compressive load will be applied to the shell. If a lower temperature is employed a greater compressive load will be applied to the shell. However, the temperature cannot be lowered to a point where the necessary compressive load will cause a permanent deformation. in the material adjacent the circumferential band. I

Shells I8 and 20 can be applied to the pressure vessel in the same manner that shell I'6b is applied to shell Iflb.

Fig. 6 illustrates the manner in which a multilayer pressure vessel can be built up by adding layers to the inner surface of a shell. Shells I00 and I60 are'fabricated similar to shells Illb and I'6b respectively with the exception that shell I00 has a larger diameter than, and is capable of fit ting over, 'shell I60. The two shells are telescoped and placed between two pressure plates 60 which are connected by means of a hydraulic cylinder 62 capable. of drawing the two pressure plates 60 together. A burner 64 and cooling rings 66 are located between the pressure plates 60 and inside of shell I60. Burner 64 is similar to burner 44 except that its nozzles are arranged on.its outer circumference so that said burner '64 will heat the inner surface of shell I6c. Cooling rings 66'are similar to cooling rings 48 except that they are arranged to cool the inner surface of shell I60. An access opening 68 is provided in one of the pressure plates 60 to provide for the passage of fuel and coolant lines to the burner 64 and cooling rings '66. Burner 64 is located adjacent one end of, shell I60 and is ignited and allowed to heat a predetermined circumferential band, similar'to the band heated in Fig. 5 to the same temperature as the band in Fig. 5. When the band has been heated to the predeterminedtemperature, the hydraulic cylinder 62 is actuated to apply a longitudinal compressive load to shell I60, which, by reason of being longer than shell Iflc'is in engagement with both plates 60. At the time the compressive load is imposed on shell I 60 the burner 64 and cooling rings 66 are started moving slowly along shell I50 so that a band having the predetermined width and temperature is in effect moved along shell I60. The compressive load acts in the same manner as the compressive load of Fig. 'and causes the heated band to be upset resulting in an increase in the outside diameter of shell I60, which in turn results in shell lEc being brought into intimate face-to-face contact with the inner surface of shell lGc.

Fig. '7 of the drawings illustrates the manner 1n which plate bending rolls are employed to successively upset longitudinal'strips along the shell lfid. Inner shell llld and outer shell 16d are placed between a set of bending rolls T0, 12 and 14, which are supplemented by rolls l6 and 18 carried by arms 80 and 82, respectively. Arms and 82 are connected to hydraulic cylinders (not shown), or any other suitable mechanisms, adapted to move the rolls l6 and 18 towards each other. An elongated oxyacetylene burner 84 is located diametrically opposite roll '12 on the outside of shell ltd and so positioned and of such a length that it can heat a longitudinal strip or area substantially the same width as the width of the circumferential band heated in the modifications of Figs. 5 and 6 throughout the full length of shell lGd.

When this longitudinal strip has been heated to the desired predetermined temperature, which is substantially the same temperature that the circumferential bands in the preceding modifications were heated, roll 12 is moved downwardly with respect to rolls ill and 14 to apply a bending moment to shell [8d around the point of tangency of shells [6d and 3d. At the same time, rolls E6 and -18 are moved inwardly to supplement and increase the bending moment established by rolls I9, 12 and M. This bending moment results in a compressive stress being set up in {Ed in that portion of Mid which is located above the rolls l0 and M, and especially in that portion located above rolls 16 and 18. This compressive stress causes shell Hid to be upset a predetermined amount by reason of uniform plastic flow of the longitudinal heated strip. As the initial longitudinal strip attains the desired temperature and rolls 1'0, i2, M, 16 and 18 are moved together to apply the bending moment resulting in the above mentioned com pressional stress, the rolls Ill, 72 and 14 are caused to rotate slowly to cause shells [0d and lfidto slowly rotate. It may be necessary, or desirable, to heat and cool the first longitudinal strip several times before rolls I0, 12, M, 15 and 18 are moved together, in the manner that the initial circumferential band in Figs. 3 through 6 may be heated and cooled, to raise the temperature of the material adjacent the heated strip to the temperature that it will be at after the process has been in operation a period of time and has reached equilibrium. The speed with which rolls 10, I2 and 14 are caused to rotate is such that shell 16d will be driven at such a speed that there will always be beneath burner 84 a longitudinal strip of the desired width having substantially the desired temperature. As shells Kid and 18d are rotated roll 22 is continuously moved downwardly with respect to rolls Ill and "and rolls l6 and ill continuously moved together so that a constant uniform compressive stress is maintained in that portion of shell ltd which is located above rolls l0 and 14.

It will therefore be seen that by maintaining a constant bending moment on shell 1541 by means of rolls Ill, '12, 14, 1-6 and 18, and continuously rotating shell lid, the upsetting of the longitudinal strips takes place as a continuous operation. It will, however, be understood that the longitudinal strips'of shell l6d can be upset intermittently by first heating a strip, setting up a compressive stress in 16d by means of rolls 7D, 12, I4, 15 and 18, followed by heatinga succeeding strip, and upsetting that, and so on until shell [Ed has been upset around its entire circumference.

Cooling bars 86 are located on each side of the burner 84 and function to keep the shell Hid on each side of the longitudinal band heated by said burner 84 cool enough 'to resist deformation by the above described compressive stress. Cooling bars 85 are preferably hollow water cooled bars, but any other suitable cooling means may be used as, for example, solid metal bars or water spray.

Any number of shells can be applied 'to the pressure vessel bysuccessively upsetting longitudinal strips thereof by means of bending rolls, and it will be understood that any desired predetermined internal circumferential stress can be set in each of these layers by varying the amount of upsetting by increasing or decreasing the compressive stresses set up by the rolls H1, 12, M, 16- and 18.

Figs. 8 and 9 illustrate the manner in which a plurality of straps or cables. 88 are employed to apply a circumferential compressive force to shell lBe to successively andv intermittently upset longitudinal strips thereof.

After shells llle and Hie have been fabricated and assembled one over the other a plurality of straps 88 are wrapped around shell lBe. To avoid confusing the drawing only two of the straps. 88 have been shown in Figs. 8 and 9, but it will be understood that a sufficient number of them are used to substantially cover the full length of shell Mic. The ends of straps 88 are attached to yokes 9D and 92 whichare attached to hydraulic cylinders (not shown), or to any mechanism adapted to exert a pull on said straps 88.

Tension is relaxed on yokes 99 and 92 and said yokes are raised or brought together to form a space 94 between the straps 88 and the shell l6e beneath the points where the ends of the straps 88 cross each other. An oxyacetylene burner 96, similar to the burner disclosed in Fig. '7, is then inserted in space 94 and the burner is ignited. The oxyacetylene burner 96 is of such a length, and has a plurality of nozzles spaced therealong, that it is capable of heating a narrowlongitudinal strip throughout the full length of shell Hie which is substantially the same width as the longitudinal strip being heated in the modification of Fig. 7. When the strip being heated has reached the desired temperature, approximately 1400 the torches are extinguished, burner 96 is removed and the above mentioned hydraulic cylinders, or other mechanism, are actuated to cause yokes 98 andSZ to separate and to draw straps BS tightly around shell 16a to set up in said shell Hie a compressive force which causes the metal in the heated longitudinal strip to be upset. It may be necessary, or desirable, to heat and cool the first longitudinal strip several times before the straps 33 are tightened, in the manner that the initial circumferential band in Figs. 3 through 6 may be heated and cooled, to raise the temperature of the material adjacent the heated strip to the temperature that it will be after the process has been in operation a period of time and has-reached equilibrium. 7

Following the upsetting of the first longitudinal strip the tension on yokes 90 and 92 is relaxed and; they are broughttogether or lifted to again provide the space 94 between the straps 88 and shell'IBe. Shells We and Hie are rotated an amount equal to, or slightly less than, the width of the longitudinal strip last upset and the burner 36 isagain inserted in the space 94 and the process repeated. 'I'he'steps of heating and upsetting succeeding longitudinal strips is continued until shell Hie has been upset throughout its'circumference. j

' It will be understood that any desired degree of circumferential compression can be established in We by regulating the tension applied to yokes 90 and 92 and thus regulating the amount of upsetting that takes place in shell "Se and this in turn as set forth above determines the circumferential pressure exerted by shell lite on inner shell lfle.

Figs. 5, 6, 7 and 8, disclose the fabrication of the cylindrical portion of the pressure vessel before the heads are attached thereto. It will be apparent to those skilled in the art that, a plurality of layers can be added to shells lllb, or We of Figs. and 8, respectively, after heads have been attached thereto, by the methods disclosed in Figs. 5 and 8, respectively.

It will also be understood that multi-layer pressure vessels can be fabricated using all of the modifications disclosed herein. For example, the first two layers could be assembled in the manner disclosed in Fig. 3; the third layer could be added in the manner disclosed in Fig. 5; the fourth layer could be added in the manner disclosed in Fig, 7; and the fifth layer could be added in the manner disclosed in Figs. 8 and 9.

The present invention has been disclosed and described in connection with the fabrication of steel multi-layer pressure vessels. It will be appreciated by those skilled in the art that multilayer vessels can be formed by means of the herein disclosed process from any thermoplastic material as, for example, metals other than steel, thermoplastic plastics, and glass.

Since certain changes may be made in the above process without departing from the scope of the invention herein involved, it is intended that all matter contained in the above description and shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.

I claim:

1. The method of manufacturing multi-layer high-pressure vessels comprising the steps of providing an inner shell'having a predetermined outside diameter, providing an outer shell having an internal diameter greater than said predetermined diameter, locating said inner shell inside of said outer shell, heating a circumferential band of said outer shell having a width not greater than three-quarters of the natural buckling wave length of the material of said outer shell to render it relatively plastic, applying a longitudinal compressive force to said outer shell of suflicient magnitude to upset said heated band by substantially uniform plastic flow to cause thev force to said outer shell to progressively reduce.

the diameter thereof.

2. The method of manufacturing multi-layeroutsid diameter, providing an outer shell hav ing an-internaldiameter greater than said predetermined diameter, locating said inner shell inside of said outer shell, heating a narrow area of said outer shell having a width not greater than three-quarters of the natural buckling wave length of the material of said outer shell to a temperature whereat it is relatively plastic, ap plying a compressive stress to said heated area of suflicient magnitude to cause it to upset by substantially uniform plastic flow of the material thereof and theinner surface thereof tocontact the outer surface of said inner shell, progressively heating substantially similar succeeding areas of said outer shell, and continuing the application of said compressive stress to progressively upset said outer shell.

3. The method of manufacturing multi-layer high-pressure vessels comprising the steps of providing an inner shell having a predetermined outside diameter, providing an outer shell having an internal diameter greater than said predetermined diameter, locating said inner shell inside of said outer shell, heating a circumferential band of said outer shell having a width not greater than three-quarters of the natural buckling wave length of the material of said outer shell to render it relatively plastic, applying a longitudinal tensile force to said outer shell of sufficient magnitude to elongate said heated band by substantially uniform plastic flow to cause the inner surface thereof to contact the outer surface of said inner shell, progressively heating substantially similar circumferential bands along the length of said outer shell, and continuing the application of said longitudinal tensile force to said outer shell to progressively reduce the diameter thereof.

4. The method of manufacturing multi-layer high-pressure vessels comprising the steps of providing an inner shell having a predetermined outside diameter, providing an outer shell having an internal diameter greater than said predetermined diameter, locating said inner shell inside of said outer shell, heating a narrow area of said outer shell having a width not greater than threequarters of the natural buckling wave length of the material of said outer shell to a temperature whereat it is relatively plastic, applying tensile stress to said heated area of sufficient magnitude to cause it to elongate by substantially uniform plastic flow of the material thereof and the inner surface thereof to contact the outer surface of said inner shell, progressively heating substantially similar succeeding areas of said outer shell, and continuing the application of said tensile stress to progressively elongate said outer shell.

5. The method of manufacturing multi-layer high-pressure vessels comprising the steps of providing an inner shell having a predetermined outside diameter, providing an outer shell having an internal diameter greater than said predetermined diameter, locating said inner shell inside of said outer shell, heating a narrow area of said outer shell having a Width not greater than three-quarters of the natural buckling wave length of the material of said outer shell to a temperature whereat it is relatively plastic, applying stress to said heated area of sufiiclent '15 magnitude to cause it to deform by substantially uniform plastic flow of the material thereof and the inner surface thereof to contact the outer surface of said inner shell, progressively heating substantially similar succeeding areas of said outer shell, and continuing th application of said stress to progressively deform said outer shell.

DAVID B. ROSSHEIM.

REFERENCES CITED UNITED STATES PATENTS Name Date Mannesman Dec. 15, 1891 Number Number Name Date Brinkman 1 Mar. 7, 1905 Broido Jan. 14, 1930 Leake July 22, 1930 Cooper July 7, 1936 Watson Oct. 22, 1940 Raymond et a1. Feb. 17, 1942 Goulding Jan. 26, 1943 Watter Feb, 15, 1944 Murray Mar. 13, 1945 Needham May 1, 1945 Gay -1 May 22, 1945 Linden et a1. Dec. 23, 1947 Rossman Nov. 2, 1948 Rossheim et a1. Aug. 30, 1949 

